It is known from Z. Liu, M. Zarki, “SIR Based Call Admission Control for DS-CDMA Cellular Systems”, IEEE Journal on Selected Areas in Communications, Vol. 12, No. 4, pp. 638-644, May 1994, from Z. Dziong, M. Jia, P. Mermelstein, “Adaptive Traffic Admission for Integrated Services in CDMA Wireless Access Networks”, IEEE Journal on Selected Areas in Communications, Vol. 14, No. 9, pp. 1737-1747, December 1996, and from S. Kumar, S. Nanda, “High Data-Rate Packet Communications for Cellular Networks Using CDMA: Algorithms and Performance”, IEEE Journal on Selected Areas in Communications, Vol 17, No. 3, pp. 474-492, March 1999, that power is a robust integral measure of the network load for WCDMA systems, supporting both speech and variable bit-rate data users. Hence, users are allowed to access the system provided that P<Pthreshold, where Pthreshold is a known power threshold obtained from network dimensioning, and P is the total transmit power from the respective Base Station (BS). Assuming that the power allocated to user number n equals Pn, then the following relation can be expressed: P=ΣPn.
In order to quantify if the same decision rule can be applied for BSs equipped with antenna arrays, the expected capacity gain from using this technology has to be considered. It is assumed that simple beamforming (BF) is used with an M-element antenna array, where a beam is created towards the desired user without considering the signals from interfering users (i.e. knowledge of the spatial covariance interference matrix is not exploited). Provided that the interference is spatially white (i.e. interference is not dependent on the spatial transmitting or receiving direction of the beam), the capacity can approximately be improved with a factor of M (assuming omni antenna elements), while no capacity gain is expected for the case where all users are positioned at the same azimuth direction. Thus, the capacity gain due to spatial filtering is very sensitive to the spatial distribution of interference, and consequently it is important that this mechanism is captured by the admission control (AC) algorithm, so that the system remains stable under all possible conditions. This is especially important for systems with mixed speech and high bit-rate data services, where the spatial interference is likely to deviate from the spatial white assumption, which normally is assumed valid for WCDMA systems supporting a large number of speech users only.